The effort by the automotive industry to reduce the weight of vehicles to thereby improve fuel efficiency has seen an increasing use of non-metallic materials in various parts of vehicles. Heat exchangers, more commonly termed radiators, are no exception. While metal materials are still employed in the cores of such heat exchangers because of their greater thermal conductivity over plastics, other heat exchanger components that do not require good thermal conductivity are being made of plastic. A primary example is the so-called tanks which are fitted to the heat exchanger core most typically by securement to the header plates which define the ends of the cores.
In a typical case, the header plate is provided with a peripheral groove and a seal or gasket is disposed in such groove. The plastic tanks include a peripheral flange defining a nominally parallel sealing surface. The tank is fitted to the header plate by locating the flange within the groove with the sealing surface compressing the seal to establish a seal at the header plate-tank interface and a variety of means are utilized to hold the components in assembled relation.
Representative prior art illustrating constructions of this sort include U.S. Pat. Nos. 4,378,174 and 4,331,201 issued respectively May 29, 1983 and May 25, 1982 to Hesse, and commonly assigned U.S. Pat. Nos. 4,531,578 issued July 30, 1985 to Stay et al and 4,600,051 issued July 15, 1986 to Wehrman.
A couple of difficulties attend the use of plastic tanks and these difficulties become aggravated as the size of the tank increases. In particular, and with reference to FIGS. 6 and 7 herein, plastic tanks are subject to two forms of deformation that may hinder assembly of a tank to a header plate in good sealing relation. One form of such deformation is so-called "suck-in" which is illustrated in FIG. 6 and the other form of such deformation is so-called "banana-ing" which is illustrated in somewhat exaggerated form in FIG. 7.
Tanks of this sort are commonly formed by injection molding and the deformations occur as the molten plastic cools and solidifies. As seen in FIG. 6, a prior art plastic tank, generally designated 10, has elongated, spaced parallel walls 12 and 14 interconnected by end walls 16 and 18. The wall 12 may include a fixture 20 for the ingress or egress of coolant and the walls 12, 14, 16 and 18, together with a peripheral flange 22, define an opening 24 in a generally trough-like configuration. About the opening 24, the flange 22 includes a nominally planar, peripheral sealing surface 26.
As can be readily appreciated in FIG. 6, and with reference to a straight line 28 drawn therein, the walls 12 and 14 have bowed substantially inwardly at locations intermediate their ends. This deformation is, as mentioned above, known as "suck-in" and may make it difficult to fit the flange 22 within the seal receiving groove in the header plate. And though not as much of a problem, suck-in may occur in the end walls 16 and 18 as well.
As seen in FIG. 7, the sealing surface 26, which is intended to be planar as indicated by a line 30, may assume a convex configuration as the entire tank 10 tends to curve like a banana, giving rise to the name "banana-ing" for this second type of deformation.
In any event, when the tank 10 such as shown in FIG. 7 is applied to a header, the gasket in the flange receiving groove of the header will be overly compressed near the center of the walls 12 and 14 and be insufficiently compressed, or even not contacted at all, in the area of the end walls 16 and 18, unless the tank 10 itself is substantially stressed during the assembly operation. In one case, a poor or nonexistent seal results and in the other, as a result of thermal and pressure cycling of the radiator when in use, the overly stressed tank and/or gasket may prematurely fail.
The present invention is directed to overcoming one or more of the above problems.